Certain large production tractors have transmissions which are shiftable among a plurality of shift or gear ranges. For example, on transmissions used in John Deere 7030 large-frame tractors, range shifts among five ranges are performed with a manually-actuated clutch arrangement.
It is proposed to perform such shifts electronically with a mechanism which includes a range-selection-shaft or shift rail which is translated axially to control the meshing of synchronizers and gears. The synchronizers and gears are fully meshed only within the last 1.0 mm of rail travel. It is therefore necessary to accurately sense the position of a range-selection-rail in order to prevent clutch engagement before the synchronizers are fully engaged with gears (an event which would cause damage to the drivetrain components). Therefore, a sensor is needed to sense when the rail has successfully made the transition into the selected range.
Because the rail must travel through a total distance of approximately 20 mm, it is not possible to accurately sense rail position throughout the entire travel range using a conventional inductive or Hall-effect sensor inline with the rail. Also, geometry constraints limit access to the end of the rail. Thus, a position sensor is needed which is displaced radially from the rail, and which can rapidly and accurately sense when the rail is within the last 1.0 mm of rail travel.